In short answer : Yes, but you shouldn't.
Long answer:
It can be used for mining, however the design of all Nvidia chip GPU's don't work well compared to ATI, due to their differences at a hardware level.
At a software level, the mining process mostly uses OpenCL to make use of the "Shaders" (hardware) on the GPU. Nvidia and ATI both have these, but Nvidia took the approach of a few complex ones and ATI too the approach of lots of simple ones. The mining process is relatively simple, thus having lots of simple shaders is very efficient for this task. Nvidia more complex shaders in some areas are less efficient and thus far there has been no way to compensate for that. There is in the region 5-10 less bitcoins generated out of a similar power (watt) consuming processor between nvidia and ati. This makes Nvidia GPU's so inefficient you actually spending money to make these bitcoins rather than turning a profit, which generally speak you will always do on an ATI GPU.
Both GPU markers, choose these different paths quiet a few years ago and ATI kept theirs when they realise they had adopted a secondary market outside of gamers, Nvidia already had the TELSA to bring in the more Scientific use of GPU so were not going to change their design.
Thanks you. For now, i will sell stuff.. maybe the next year i will buy one of these ATI cards. Wich one its better for mining?
This wiki, keeps track of popular mining cards and the results from them.
https://en.bitcoin.it/wiki/Mining_hardware_comparison#Popular_Mining_CardsGenerally speaking the 5xxx series has been very popular and now retains a good amount of value since they haven't devalued much in the last year. However the 7xxx series (latest series) is a bit more efficient, however they will devalue by next year, possibly ruining it's resell value if that is something you plan to do (many do). So by next year you can probably pick up a 7970 for a good price. It changes all the time, so their is no good answer that far ahead.
Also by next year, FPGA and ASIC could become more mainstream, due to a change in difficulty of the blocks and reduction in value from them, so buying GPU's for the purpose of mining might not be ideal any longer.